1. Field of the Invention
The present invention relates to a method for recognizing knocking of an internal combustion engine, preferably of a gasoline engine, in which solid-borne sound signals are measured and solid-borne sound features are recovered from them; and to an apparatus for carrying out the method.
2. Description of the Related Art
In gasoline engines it is usual to detect knocking by way of a knock sensor. This knock sensor is disposed on the gasoline engine and recognizes solid-borne sound vibrations of the gasoline engine that occur as a result of explosion-like combustion events inside the cylinder of the gasoline engine. These explosion-like combustion events occurring inside the combustion chamber of the gasoline engine are converted into vibrations that are conveyed to the walls of the internal combustion engine and are perceived there as solid-borne sound. Excessive vibration can result in damage to the gasoline engine and must therefore be suppressed.
For knock recognition, the solid-borne sound signal supplied from the solid-borne sound sensor is in essence filtered, rectified, and integrated in a suitable measurement window. Based on the final integral value, a relative solid-borne sound feature is then calculated, and with this a knock decision is arrived at by way of a threshold value comparison.
Interference is increasingly presenting problems with this type of knock recognition. In order to improve knock recognition, the possibility exists of calculating a time/frequency representation in the measurement window, with the result that a plurality of solid-borne sound features for a combustion event are ascertained. It is still unclear, however, how classification in a high-dimensional space is to be accomplished based on such a plurality of solid-borne sound features. There are known methods, such as support vector classification (SVC), with which a classification in high-dimensional space can occur. This method is not optimal for knock recognition, however, since only digital decisions can ever be made here, whereas the knock intensity represents a continuous signal. Support vector regression (SVR) is also known, but this has the disadvantage, at least in the standard application, that the weighting of individual elements is always the same.